1. Field of the Invention
The present invention relates to a multi-function valve assembly for use in a single cavity, which is particularly suited for use in an inflatable packer system. Inflatable packers are used, among other things, to isolate a zone in an uncased wellbore; to isolate a zone between the casing and the formation in a cased wellbore; or to isolate a zone between outer casing and interior or intermediate casing. A particular use is to sealingly isolate the annulus between casing and wellbore in a cased well for cementing operations, and similarly in pile grouting operations.
2. Description of the Prior Art
Efficient use of an inflatable packer requires a valve system which accomplishes the following:
1. Prevents inflation of the packer until a certain desired pressure in the casing is reached. PA1 2. Permits the packer to inflate to a desired pressure. PA1 3. Prevents the packer pressure from exceeding or falling below a certain desired level called the "setting pressure." PA1 4. Isolates the casing pressure from pressure in the well annulus. PA1 1. the control piston is fully guided; PA1 2. design variations are possible, e.g. the use of varying differential area; PA1 3. seals and "O" rings never pass directly over a cutting edge; PA1 4. the need for multiple cavities and flow paths is eliminated; PA1 5. the need for multiple independent valves is eliminated; PA1 6. and accurate operation is made possible.
The Lynes ECP, the Xenpax Casing Packer, and the CTC Inflatable Casing Packer disclose valve systems which are typical of the prior art. In each of these prior art systems a plurality of valve mechanisms are employed to achieve the multiple purposes of an efficient system. The use of a plurality of independent valves requires a plurality of fluid flow paths or cavities between the casing, the annulus, and the interior of the inflatable packer. In short, the prior art inflatable packer valve systems are complicated, inefficient, and require expensive drilling of fluid flow paths or cavities. In addition to these considerations, various problems have been encountered with the prior art systems. Various prior art packers inflate prematurely or over-inflate due to the use of improper, defective shear pins or the use of incorrectly sized differential areas. In the prior art packers, if the packer element fails, the casing is not isolated from the annulus and unwanted communication of fluid from the casing to the annulus and vice-versa occurs. In the prior art systems using cross-drilled holes and valve pistons or stems which employ sealing "O" rings, the "O" rings can be damaged or completely severed by movement across the edges of the multiple cross-drilled holes.